Adding users

This will seem like the stupidest question in history bu bear with me. Just got a hold of a RadyNAS104. Drives in, software updated, all looking good.  Until I come to add users. Added one. Didn't appear in list. Try to add it again and it told me it either existed or was reserved (it is only my name, which is not root or admin!). Tried a longer version of my name, still nothing on screen. But again still exists after another go. SO tried someone else in the house. Bingo - name appears. So apart from it telling me it hates me, what is going on? Thanks in advance for any help.